This invention is concerned with the detection of electromagnetic radiation. In particular, a wide variety of scientific, medical, industrial, and military applications require the detection of infrared (IR) radiation. The field of IR photoconductive detectors was significantly advanced with the development of impurity band conduction (IBC) devices. These devices, including the Blocked Impurity Band (BIB) detector (described in Petroff, et al., U.S. Pat. No. 4,568,960) and the Solid State Photomultiplier (SSPM) (described in Petroff, et al., U.S. Pat. No. 4,586,068), exhibit improved performance compared to earlier photoconductive detectors. IBC detectors have been fabricated in silicon using either arsenic or gallium dopant atoms with concentrations approximately an order of magnitude greater than had been practical with prior photoconductive detector designs. These high concentrations of majority dopant atoms enable the construction of a thin detector with high quantum efficiency, reduced sensitivity to nuclear radiation, and none of the irregular electrical characteristics found in the photoconductors of the prior art. The SSPM, whose design builds upon the improvements achieved by the BIB detector, is capable of continuously detecting single photons.
IBC devices were originally developed primarily for applications requiring long wavelength infrared (LWIR--approximately 5 to 30 micrometers) photon detection. It would be desirable, however, to extend the quantum efficiency of these impurity band conduction devices to shorter wavelengths for which the absorption length is significantly greater that the thickness of the active layer of the device.